The present invention relates to a dielectric ceramic composition having a high relative dielectric constant (.epsilon.r) and a small and widely controllable temperature coefficient of resonance frequency (.tau.f).
Recently, ceramic filters have been widely used for movable radio transmitters and receivers such as automobile telephones and cordless telephones operable at microfrequency bands from MHz to GHz. This is due to the fact that the dielectric materials constituting the ceramic filters have high dielectric constants (.epsilon.r) and quality factors Q under no load (Q.sub.0), and that their temperature coefficients (.tau.f) of resonance frequency are freely controllable on both the positive and the negative sides from 0 by changing the compositions of the dielectric materials.
Conventional dielectric materials are, for instance, MgO--CaO--TiO.sub.2, ZrO.sub.2 --TiO.sub.2 --SnO.sub.2, and BaO--TiO.sub.2 -lanthanoid oxide, etc.
However, these dielectric materials have relative dielectric constants (.epsilon.r) less than 100, and the miniaturization of resonance elements formed from them is inherently limited.
Therefore, there is a strong desire for dielectric ceramic compositions with high relative dielectric constants (.epsilon.r).